Randy Thornhill interviewed by Emma Taylor on January 24, 1996 "More symmetrical men fire more copulatory orgasms." Randy Thornhill is a professor of biology at the University of New Mexico. His recent research concludes that the female orgasm is more likely and more frequent when the sexual partner is symmetrical. Tripod: Why did you decide to test this theory? What made you think that there might be some correlation between male symmetry and the female orgasm? RT: In a wide variety of organisms now, both plant and animal, it has been shown that symmetry correlates with important aspects of performance. The work we've been doing on humans has looked at the role of symmetry in men's sexual history. We find that body symmetry in males correlates with number of sex partners in a lifetime, it correlates with the age at which men begin sexual intercourse. More symmetrical men have more partners, and they begin sex at an earlier age. We've been studying romantically involved couples, and male symmetry also correlates with the number of copulatory orgasms that the women have, and other aspects of the man's behavior in these relationships. For example, more symmetrical men engage in more infidelity, outside the relationship. The idea is basically that what symmetry is, is a reflection of good design for the environment in which you develop, and should therefore be correlated with performance, such as longevity, mating success in males, and so forth. Tripod: How do you define symmetry in a man? RT: Well, we measure body features. We do facial symmetry, and we do non-facial body symmetry. Facial symmetry is done using computer techniques that we have developed here. Body symmetry is based on features such as elbows, hands, wrists, ankles and feet -- you measure it on both sides. The difference between the left and the right is the individual's asymmetry on that trait. Then we combine those asymmetries into a body asymmetry index for each individual. Tripod: But how many women really notice a man's elbows? RT: These are not signals themselves, with the exception of facial symmetry. We look at facial symmetry, and it is an aspect of facial beauty ... But most of these asymmetries that we're talking about are very small differences between left and right -- that we all have, it's just a matter of degree. We don't, indeed, inspect, the difference in size between the left and right wrist, and so forth, in our decisions to choose mates. But these symmetry measures reflect the quality of the individual, the value of the individual as a mate. Therefore, you get the correlations. Tripod: How many couples did you test? RT: For the orgasm study, we looked at a sample of 100, and 86 of those were having sex, so those were the ones we used. In our other studies, where I mentioned the infidelity and all that, we've looked at around 200 couples. Tripod: When you're looking at the female orgasm, how accurate can your data be? Aren't both men and women likely to lie, or at least exaggerate? RT: Oh yes, that's in there, of course. The way we handle that methodologically, is we ask the man to report on his experience, separately and privately, in a questionnaire. These are not interviews -- you can't get good data on explicit sexual stuff from interviews. But you can put a person in a room, and they don't have any idea what you're going to ask them, and give them a questionnaire. So you ask him about his experience with the female, in terms of her orgasm frequency during copulation. Separately and independently, the female is in a room, filling out the same questionnaire. So the men provide an observer reliability for the female, the female gives her answer to the questions. And they do indeed correlate highly. So that tells us a bunch of stuff. It tells us that men are really keen on their women's sexual response -- as we anticipated -- and as you expect, if female sexual response is a female choice mechanism, basically. Men will track that information. So we used the female responses and the male responses -- we can use either set of those data and get the pattern that we're talking about here today. That is, more symmetrical men fire more copulatory orgasms. Tripod: What were the results, in terms of correlation? RT: The way you work it is, statistically, you have a number of variables that you think might affect female orgasm frequency. One of those is male body symmetry. Another might be male socio-economic status, another might be number of sex partners that a man has had -- which certainly tells you something about sexual experience of the male. So we have these variables that we want to look at in relation to female orgasm frequency. Of these variables that we have looked at, the only predictor of female orgasm frequency during copulation is male body symmetry. "Predictor" means that it statistically, significantly correlates with female orgasm frequency. Tripod: The female orgasm increases the likelihood of conception, right? RT: Yes, that's true, so the orgasm works as a selective mechanism. If the female does not orgasm, or, if she orgasms before the male places his ejaculate in her vagina, she has low sperm retention. The effect of female orgasm in retaining sperm has been measured by my colleagues in England. Tripod: Given that the female orgasm serves no biological function, does this new research throw any light on the mystery of the female orgasm? RT: Oh indeed, indeed. It indicates that female orgasm is an adaptation for selective sperm retention. Tripod: Can these results be useful for couples? RT: Well, my take on all this is that the more one knows about oneself, the better off one is, including the more you know about your own sexual emotions. Women, and people in general, have been trying to understand orgasm ever since the beginning of time, and there's tremendous literature on female orgasm, a lot of writing, but no answers. We're beginning, we hope, to get a handle on what it's all about. Tripod: What has been the general reaction to this research? RT: A lot of interest. Tripod: No skepticism? RT: Well, there's healthy scientific skepticism, and we have it too. There are lots of things that want to follow up, and will do so, in subsequent work. It's possible that really what we're looking at here is an important faux factor. These symmetrical men may smell better to females, and that's a realm that we haven't explored yet, but we're planning to. Do symmetrical men smell better to females? And does this increase the woman's orgasm response? That's one avenue that we want to explore. Tripod: Were the couples you tested surprised by the results? RT: Some, yes, definitely. But in general, we have found that the people involved are curious about themselves, and like participating in a science project like this, especially one dealing with such important matters as their personal sex lives. Tripod: I was just wondering, do you know what your name, Randy means in England? Quite appropriate for your line of work. RT: Yeah. [laughs] I've spent a lot of time in England.